This invention relates to a catalyst component in the form of solid particle which has attractive properties as the carrier of a catalyst for olefin polymerization. In general, it is desired that the carrier of a catalyst for olefin polymerization have a relatively large particle size and a relatively narrow particle size distribution which are characteristics that are particularly sought in catalysts for use in gas phase polymerizations. It is known to polymerize alpha olefins, such as ethylene, using a catalyst component comprising titanium on magnesium halide or magnesium alkoxide support, the component being obtained by either copulverization or by direct reaction with a liquid titanium compound containing halogen. Such a component is then used in the polymerization reaction with a trialkylaluminum cocatalyst, e.g., triisobutylaluminum.